Our web front ends are spiking quite often to 99%. I have looked at the worker process in IIS and noticed a pattern of the requests coming in.
We have a user that has been adding web parts for list views on pages and setting them up to be async, with a refresh every 30 seconds. So far, it looks like there are about 35 web parts across multiple pages set up this way, and a handful are probably opened by multiple users and left open for sustained periods of time.
Would this account for CPU spikes on the WFE? Our two WFEs have 16MB RAM and quad 2.8 Ghz Xeon processors, running on VMware.
I did some testing in google chrome debugger with one of these pages, and after the initial load there were 60 post requests from the page @ 14.4mb in a five minute period.
I don't want to suggest to the user to limit the use of the ajax option if that wouldn't normally cause performance issues.
EDIT: I found more, now the total is 48 web parts with auto refresh on.